The study of the protein complement of an organism, termed proteomics, has emerged as an important approach for identifying drug targets and new drugs. The field of proteomics includes two approaches: expression proteomics, which studies global changes in protein expression, and cell-map proteomics, the systematic study of protein-protein interactions (Blackstock et al. (1999) Trends in Biotechnology 17:121-127). Unlike the fixed genome, the proteome is a dynamic entity reflecting gene expression, stability and post-translational alterations. The proteome may be cell or tissue specific, and be affected by the metabolic state, health, and environment of the organism.
Current methods for monitoring global gene expression primarily rely on gene-chip/DNA microarray technology. Another approach for studying the expression of proteins in a cell entails the use of high-resolution 2-dimensional (2D) gel electrophoresis.
Ubiquitin (Ub) is a 76 amino acid protein that is highly conserved in eukaryotes, and is covalently linked to other proteins to mark them for degradation by a protease called the proteasome. Non-proteolytic effects of protein ubiquitination have also been described. Rad23 is a highly conserved protein involved in nucleotide excision repair. Human Rad23 contain amino-terminal ubiquitin-like (UbL) domains that &an bind the proteasome (Schauber et al. (1998) Nature 391:715-718).